Vapor phase hydrogenation of nitrosodialkylamines



assignorsto Allied Chemical Corporation New York,

; United S at m -ic I V, p 1 3,133,120 Patented May 12,191.64

; a ,133,120 .t V

VAPOR PHASE HYDROGENATIGN OF I; -NITROSODIALKYLAMINES. I v st Gaskins and EdwardJ. Buyalos, Hopewe'lL- Va.,

N.'Y., a corporation of New York r 3 Filed Nov. 19,1959, SeLNo. 854,151

' 1' cal-dialkylhydrazines in which the alkyl groups each conto 200 p.s.i;g. and at a temperature of from 80 to 165 C., preferably. 85 to 100 C. g V 7 .It is important that a large excess of hydrogen be used. The use of alargeexce ss ofhydrogen, namely at least 20 rnols of hydrogen per mol of nitrosodialkylamine under the conditions of pressure and temperature above given and employing a platinum catalyst results in highyields and productivity rates and permits the conduct of the reaction in the vapor phase.

,ltainfrlom. 1 to'3 carbon atoms and specifically to the .pro-

' duction of unsyrrimetrical dimethylhydrazine, herein .re-

gferredf'to for the sake of brevity as-DM'H. More particular1y, this invention relates to the" catalytic hydrogenation pf nitrosodimethylamine to produce DMH. While the invention'will be hereinafter described, for the most. part,

f'in. connection with the production of the preferred emfbodiinent, D-MI-I, itwill beundrstood it is not limited thereto and includes the preparation .of unsymmetrical-dialkylh'ydrazines such as diethyl-Qdipropyl, unsymmetricalmethyl 'ethyL, and unsymmetrical-ethylpropylhydrazines.

DMH is used as a special fuel in the guided 'missileand I rocket fields... Reduction. of nitrosodimethylamine to DMI-I by treatmentwith metallic zinc and aceticacid or The'process is carried out by introducing the nitrosodimethylamine along with hydrogen into a vaporizer and passing theresultant vapor mixture through the catalyst 'bed at a vapor space velocity of from 40 tof 2,000 reciprocal hours, preferably ,from 50 to 500, reciprocal hours, based on the nitrosodimethylamin'e at 'STP (0? C. and 760 mm. of mercury). Desirably an aqueous s'o-' luti'on' of nitrosodin iethylamine is fed to the'vaporize'r for economic reasons to aid in. the volatilization of the nitrosodimethylamineat relatively low temperatures.- Inaluminum and caustic soda, expensive reducing agents,

has been suggested. In recent years, much ettort has been I {devoted to the development of hydrogenation procedures .for reducing "nitrosodimethylamine to. DMI-L; All .pro

.cedu'res heretofore suggested, to the best of our knowledge ,andbelief, have involved liquid phase procedures under high pressures employing catalysts such as platinum, pal

.ladium or -Raney nickel. For example, .Brit is hPa tent 8 01,534fof 1958 refers to thevusef'of hydrogen. pressures between 1,200 and 2,000 p.s.i. g. and sta'testhat optilrlurr'lv xresultsare obtained at about-l-,600"p.s.i.g. Such'procedures for reducing nitrosodialkylamines are; objectionable for a,number of reasons, among which may be mentioned,

1 require expensive autoclaves orother'costly. pressure equipment DMH yields andlproductivity rates are ",relatively low.

7 It isaprineipal 'object J yide a catalytic process of hydrogenating nitrosodialkyl- V amin'es. having from -1 to 3 carbon atoms in the. alkyl groups, particularly nitrosodimethylamine, 'whibh can be 1 carried out. at relativelyllowpressures. and" hence requires v for its practice inexpensive low pressure equipment;

Another object of thisinvention is to providesuch '3 P QCess inwhich tlrle reaction carried out infth i PQ c- Pb se ith high yields and frelatively.high qd .tivity' rates;

etofore known liquid phase processes.'in-- Other 'objects' 'and advantagesjei this invention will;

arent; from the following detailed description thereof.

6f the present invention to prostead of an aqueous; solution, the nitrosodimethylamine may be dissolved in other-suitable solvents, such, for

example, as acetica'cid, ethyl alcohol, methyl alcohol,

thereof without water."

Preferably the catalyst'isasupported catalyst; activated alumina desirably is used .as the support." Such catalyst can be produced, for example, by coating'the support with the platinum metal toprovide a supportedcatalyst containing from 0.1% to 5%,preferably 0.l% to-.2%,

by, weight of the metal on the carrier particles. For ex-' ample, a platinum salt, such as platinic chloride, may be deposited on activatedalumina particles havingasize of from 4 ,t0 mesh (U screen: size), the .thus coated p r cl s. e ma ed ,Wthiw um h s x l nd platinum oxide thus formedreduced to platinum. Alternatively; platinum may beidirectly depositedon the carrier particles, V V a 'In the accompanying;drawing-the single'figure shows diagrammatically, for purposes of exemplification. and to facilitate a better understanding of thisinvention, a preferred arrangement-of equipment for carrying out the process ofthisinyention. e v In this drawing, 10indicates a vaporizer which-may hex-fof any well known type. and which .in operation is heated to atempei'ature of 'frorn to 165 C., preferably to C.,and is maintained at a pressure above atmospheric, preferably 75 to 200v p.s.i.g. 1A .solu- -tion"of nitrosodimethylamine, preferably aqueous, convide such catal se amass in..which the catalyst has rela tively long life,:appreciablylongerthan the lifeof-the .ieat'alysts -volving the, passage, of-hydrogenand the nitros'odialkyl- 1 ,Cthrou'ghva catalyst bed 15 contained in the catalyst reactor 0 accoidancewith thep'resent invention, nitro sodia'lkyl;

N amines in which the, alkyl: groups contain frlo r n I to: 3 ,f carboif atoms, particularly nitrosodme'thylamine;are V 'drOgen'ated produce unsymmetrical dialky-lhydraaines,

jga"rtieull'arly passing the nitrosodiallryl amines in 'fi l i qrl rhas j hdfhv ssts m o s lea QmQ Yof h drogenper ghol of nitrosodiall ylamine,. desirably Kin er amass l r ss i b tg t atit .id r hly not exceeding about" 500fp.'s.i.g. 'andpreferably fronr'75 .taim'ng from 10% to 75% nit rosodimethylamine and, 25% 'to'90% solvent is pump'edinto the vaporizer v.10 by. .a pump 11 through line 12.. Hydrogen. is supplied to 1 8 ill another. object of thelpresen-tinventionis .to.p'rovaporizer 10 through line 13 byv pump'14.} The .riitrosodimethylamine and water vaporize in'vaporizer 10and mix with the hydrogen, the reactants being supplied in a ratio-of 20 to. 600-mols of hydrogen-periirr'ol of,nitrosodi- .niethylamine. q:

From the vaporizer 10,: the vapor 'mixture. passes. up

16; communicablyconnected with vaporizerlll byline 17. The catalyst bed is 4 thus 1 maintained under :a. hydrogen pressure above atmospheric. Catalyst bed1 5 is composed offplatinum catalyst particles. The reaction mixture in the vapor phase leavesthe catalyst reactor lfi'thr'ough line 18 and enters the partialcondenser-'19: Condenser 19 feffects partial condensation-off-the dimethylhydrazine' lalo ng' with 'water-and 'by-products formed, 'chieflyjdimetb V ylarnine-and ammonia? Residual -reaction gases are scrubbed with water by passage .throughscrubber 21' where remaining. dimethylamine, ammoni'a, dimethylhydrazine and ,water'jar'e removed from the' hydrogen gas stream. jThe' ihydrogen exitsfrom scrubber 21 through] line 22 and may be recycled t'o the pump 14 and fed to 3 3 thevaporizer under desired pressure. is collected in the receiver 23.

Vaporizer 10 and the catalyst reactor 16 may be of stainlesssteel orother materials resistant to corrosion by the reactants and the reaction products. Since the operating pressures do not exceed 500 p.s.i.g. and preferably are within the range of from 75 to 200 p.s.i.g., relatively inexpensive low pressure equipment may be used.

The following examples are illustrative of the process of this invention. It will be appreciated that this invention is not limited to these examples. In the examples, parts and percentages are on a weight 'basis, temperatures in C. The examples were carried out in equipment of the general type shown in the drawing. V

The crude DMH Example I V An aqueous solution containing 53% nitrosodimethylamine was fed to the top of the vaporizer where it was vaporized and mixed with hydrogen in a mol ratio of 85 mols of hydrogen per mol of nitrosodimethylamine. The vaporizer'was maintained at 87, the reactants passed down through the vaporizer and the resultant vapor mixture was passed up through a catalyst bed in the catalyst reactor at a vapor space velocity of 60 reciprocal hours based on the nitrosodimethylamine at STP. The catalyst bed was composed of 0.43% platinum on 8 to 14 mesh activated alumina. It was maintained under a pressure of 100 p.s.i.g. The reactants entered the bed at 88; the maximum temperature within the bed was 95.

The reactor effluent from the catalyst reactor was partially condensed by cooling to and then passed through Water scrubbers. Analysis of the resulting aqueous solution showed that the reaction product contained:

Component: Percent DMH 34.4 Dimethylamine V 4.3 Ammonia 1.6 Nitrosod-imethylamine 3.6 Water 56.1

A" yield of 80% of DMH was thus obtained based on the nitrosodimethylamine fed to the catalyst reactor.

7 V Example II 4 V as the disclosed conditions of proportions, temperatures and pressures are maintained.

It will be noted that the present invention provides a process for synthesizing dialkylhydrazines, particularly DMH, involving the passage of the dialkylnitrosoamine in the vapor phase admixed with hydrogen through a bed of platinum catalyst particles at pressures from just above atmospheric to 500 p.s.i.g., preferably from 75 to 200 p.s.i.g., and temperatures of from 80 to 165 C., preferably 85 to 100 C. Accordingly the process can be carried out in inexpensive low pressure equipment. The present process is advantageous not only in that it results in high yields and productivity rates involving as it does a vapor phase hydrogenation of the nitrosodialkylarnines, but alsoin that the temperature conditions within the catalyst reactor can be controlled more readily in the The reactants passed through the catalyst bed at a vapor space velocity of 75 reciprocal hours based on the nitrosodimethylamine atSTP. The reactor was operated at a' pressure of 100 p.s.i.g. The reactants left the vaporizer at 86 and passed up through the catalyst bed; the maximum temperature within the catalyst bed was 92 The reactor efiluent was partially condensed, and the residual gaseous mixture passed through water scrub'bers. The condensate was combined with the product recovered in the water scrub bers. 'Analysis of the resulting aqueous solution showed that the reaction product contained:

A yield of 87.5% of DMH was obtained based on the nitrosodimethylamine fed to the catalyst reactor.

It is preferred to employ highly concentrated or essentially pure hydrogen but diluents may be present so long present vapor phase process as compared with liquid phase procedures. The catalyst remains active for long periods of time of the order of 100 hours to 1,000 hours and longer. This attribute of the process is particularly notable with the use of the large excess of hydrogen, i.e. at least 20 mols of hydrogen per mol of nitrosodialkylamine at a reaction temperature of from 80 to 165 C.

It is to be understood that this invention is not to be restricted to the present disclosure otherwise than as defined in the appended claims.

' What is claimed is: I

1. The process of hydrogenating nitrosodialkylamines to produce unsymmetrical-dialkylhydrazines, in which the alkyl groups contain from 1 to 3 carbon atoms, which process comprises passing the nitrosodialkylamine in the vapor phase and hydrogen in the proportions ofv at least 20 mols of hydrogen per mol of nitrosodialkylarnine through a bed of platinum catalyst while maintaining the catalyst bed under superatmospheric hydrogen pressure and at a temperature within the range of from 80 to 165 C. and removing from the catalyst bed, in the vapor phase, the reaction mixture containing the unsymmetricaldialkylhydrazine.

2. The process of hydrogenating nitrosodialkylamines to produce unsymmetrical-dialkylhydrazines, in which the alkyl groups contain from 1 to 3 carbon atoms, which process comprises passing the nitrosodialkylamine in the vapor phase and hydrogen in the proportions of from 20 to 600 mols of hydrogen per mol of nitrosodialkylamine through a bed of platinum catalyst while maintaining the catalyst bed under superatmospheric hydrogen pressure within the range of from to 200 p.s.i.g. and at a temperature within the range of from to C. and removing from the catalyst bed, in the vapor phase, the reaction mixture containing the unsymmetrical-dialkylhydrazine.

3. The process of hydrogenating nitrosodimethylamine to produce unsymmetn'cal-dimethylhydrazine, which process comprises passing nitrosodimethylamine in the vapor phase and hydrogen in the proportions of at least 20 mols of hydrogen per mol of nitrosodimethylamine through a bed of platinum catalyst while maintaining the catalyst under superatmospheric hydrogen pressure of. up to about 500 p.s .i.g. and at a temperature within the range of from 80 to 165 C. and removing from the catalyst bed, in the vapor phase, the reaction mixture containing the unsymmetrical-dimethylhydrazine.

5. The process of hydrogenatiug nitrosodimethylamine to produce unsymmetrical dimethylhydrazine, which process comprises continuously introducing an aqueous solution of dimethylnitrosoamine containing from to 75 weight percent dimethylnitrosoamine and to 90% .Wat'er and hydrogen in the proportions of from 20 to 600 7 through a fixed bed of catalyst consisting of supported platinum on an activated alumina carrier having a particle size of from'4'to SOmesh, the'amount of platinum on the a 6 7 carrier particles being from 0.1% to 5% by Weight While maintaining the catalyst bed under a hydrogen pressure of from to 2 00 p.s.i.g. and at a temperature of from to C., continuously removing the reaction products in the vapor phase from the catalyst bed, and recovering the unsymmetrical dimethylhydrazine from the reaction products. a Y

References Cited in the file of this patent FOREIGN PATENTS' 

1. THE PROCESS OF HYDROGENATING NITROSODIALKYLAMINES TO PRODUCE UNSYMMETRICAL-DIALKYLHYDRAZINES, IN WHICH THE ALKYL GROUPS CONTAIN FROM 1 TO 3 CARBON ATOMS, WHICH PROCESS COMPRISES PASSING THE NITROSODIALKYLAMINE IN THE VAPOR PHASE AND HYDROGEN IN THE PROPORTIONS OF AT LEAST 20 MOLS OF HYDROGEN PER MOL OF NITROSODIALKLYAMINE THROUGH A BED OF PLATINUM CATALYST WHILE MAINTAINING THE CATALYST BED UNDER SUPERATMOSPHERIC HYDROGEN PRESSURE AND AT A TEMPERATURE WITHIN THE RANGE OF FROM 80* TO 165*C. AND REMOVING FROM THE CATALYST BED, IN THE VAPOR PHASE, THE REACTION MIXTURE CONTAINING THE UNSYMMETRICALDIALKYLHYDRAZINE. 